This invention relates generally to refining apparatus. More particularly, the present invention relates to apparatus for shredding pulps.
Nowadays most of the refiners built are of twin disc design. The disadvantages of the twin disc refiner are the changing relative speed along the length of the refining zone, a relatively high idle running rating and problems with centering the rotor, particularly at low throughputs. Conical refiners are also used, whose most significant disadvantages are the poor pumping effect. This leads to throughput difficulties and, as a result, the need to enlarge the grooves in the refining zones, which reduces the edge length. The relative displacement of the knives when being set in relation to one another, the need for a sturdy design as a result of the bearing forces occurring, and the difficulties in changing the refiner plates can be considered further disadvantages.
Another type of refiner known is the so called cylindrical refiner, as described in U.S. Pat. No. 5,813,618, for example. With this type of refiner, some of the disadvantages mentioned can be avoided, however it is important to ensure that the knives are set evenly in order to guarantee the same gap and thus, the same refining conditions over the entire circumference and along the lengths of the axial refining zones.
The refiner according to the invention is thus characterized by the refining gap being set by wedges which are mounted on the stator and rotor and can be moved against each other. This causes an axial movement, of the same dimension over the entire circumference, to be converted into a corresponding radial movement. This principle guarantees that the knives have exactly the same setting.
An advantageous further development of the invention is characterized by an axially movable wedge carrier being provided.
A favorable further development of the invention is characterized by a radially movable wedge carrier being provided. This wedge carrier permits the corresponding axial movement to be converted into a radial movement, thus allowing the refining gap to be set exactly.
A favorable configuration of the invention is characterized by the gap being continuously adjustable between 0 and 2 mm, preferably between 0 and 1 mm, for example between 0 and 0.5 mm. Thus the refining gap can always be set in an optimum way to suit the properties of the pulp suspension.
An advantageous configuration of the invention is characterized by the gap being suitable for setting up to 15 mm. Thus, it is possible to avoid any damage to the refiner plates, also during start-up operations or if larger particles suddenly appear.
A favorable further development of the invention is characterized by the relative speed at the periphery being 15-35 m/sec., preferably 20-30 m/sec.
A favorable configuration of the invention is characterized by the rotor speed being between 400 and 1,800 rpm, preferably between 500 and 1,000 rpm.
An advantageous further development of a refiner with twin rotor according to the invention is characterized by two wedges being provided at the axially movable wedge carrier and whose inclined surfaces slide over the corresponding surfaces of the radially adjustable wedge carrier.
An advantageous configuration of the invention is characterized by the radially movable wedge carrier being divided into segments of a circle.